1. Field of the Invention
The present invention relates to biofuel cells of sugar-oxygen type, for example, glucose-oxygen cells, that is, fuel cells capable of converting part of the power available in a biodegradable substrate into electricity.
2. Discussion of Prior Art
Various types of glucose-oxygen biofuel cells are described in prior art, for example, in patent application PCT/FR2009/050639 (B8606). In such known biofuel cells, each electrode, anode and cathode, corresponds to an enclosure containing a liquid medium into which an electrode wire is plunged. The anode and cathode enclosures are delimited by membranes capable of being crossed by hydrogen and oxygen but preventing the circulation of other heavier elements.
The anode comprises an enzyme and a redox mediator in a solution. The enzyme is capable of catalyzing the oxidation of sugar and is for example selected from the group comprising glucose-oxidase if the sugar is glucose and lactose-oxidase if the sugar is lactose. The redox mediator has a low redox potential enabling to exchange electrons with the anode enzyme and is for example selected from the group comprising: ubiquinone (UQ) and ferrocene.
The cathode also comprises an enzyme and a redox mediator in a solution. The enzyme is capable of catalyzing the reduction of oxygen and is for example selected from the group comprising: polyphenol oxidase (PPO), laccase and bilirubin oxidase. The redox mediator has a high redox potential enabling to exchange electrons with the cathode enzyme and is for example selected from the group comprising: hydroquinone (QHD) and 2,2′-azinobis-(3-ethylbenzo-thiazolin-6-sulphonate) (ABTS).
Reactions of the following type then occur at the anode and at the cathode:

these reactions being provided in the specific case where the sugar is glucose, the anode enzyme is glucose oxidase (GOX), the anode redox mediator is ubiquinone (UQ), the cathode enzyme is polyphenol oxidase (PPO), and the cathode redox mediator is quinhydrone (QH2). A 20-mV anode potential and a 250-mV cathode potential are then obtained, which results in a 230-mV zero-current potential difference of the biofuel cell.
Such biofuel cells operate properly but, especially relating to the biofuel cell described in patent application PCT/FR2009/050639, they require for the anode and cathode conductors to be plunged into enclosures containing suitable liquids, which is a practical disadvantage in many cases and makes it in particular very difficult, or even impossible, to implant such biofuel cells in a living being.
Indeed, such biofuel cells are attempted to be implanted in living beings, especially to power various actuators, such as pacemakers, artificial sphincters, or even artificial hearts.
Biofuel cells with solid electrodes have been provided. However, biofuel cells using such electrodes, especially when they are implanted in a living being, have a very short lifetime.